In a large number of electronic signal transmission systems, and notably in portable telephones, the antenna provided for transmission and reception of signals is retractable (for reasons of compactness when the system is inoperative). To this end, the antenna rod is guided during its insertion or retraction, in a semi-rigid tube, for example of synthetic resin material, accommodated in the system (in the example described, in the portable telephone), generally above the electronic card. During assembly of the antenna and the tube in the housing of the system, the end of the tube may damage the electronic components fixed on said card, and notably the contacts to which the antenna is connected.